A so-called RTM (resin transfer molding) method has been known as a method for producing a fiber-reinforced composite body with excellent productivity. In the RTM method, in a shaping mold, a fiber base is impregnated with a matrix resin and then the matrix resin is hardened to produce a fiber-reinforced composite body (an FRP molded article). For example, in a case where a relatively large FRP molded article or the like is produced by the RTM method, generally the fiber base is preliminarily formed into a shape similar to a desired shape of the FRP molded article. Thus, a preform is preliminarily prepared from the fiber base as a molding precursor for producing the FRP molded article. The final product of the FRP molded article can be produced highly accurately and efficiently by placing the preform in a shaping mold and by performing the impregnation and hardening of the matrix resin as described above.
Specifically, for example, as proposed in Japanese Laid-Open Patent Publication No. 2008-132775, the preform can be prepared by integrating a sheet of a fiber base containing oriented reinforcing fiber pieces with a resin material or the like and by shaping the integrated sheet. Thus, for example, the reinforcing fiber pieces can be prevented from being separated from each other in the shaping step by adding the resin material to the fiber base to fix the reinforcing fiber pieces.